All optical nanoscale sensor

The composition of claim wherein the nanoparticle comprises a shell surrounding a core material with a lower conductivity than the shell material, and the thickness of the core material and the shell material is engineered to generate a plasmon resonance frequency.

A method comprising:

• associating an adsorbate with a nanoparticle, wherein the nanoparticle comprises a shell surrounding a core material with a lower conductivity than the shell material and the adsorbate displays at least one chemically responsive optical property;
• and
• engineering the nanoparticle to enhance the optical property of the adsorbate, wherein the chemically responsive optical property comprises a surface enhanced Raman scattering (SERS) spectral response that is a function of pH over at least 5 pH units and wherein the adsorbate comprises more than one pH sensitive functional group.

A method comprising:

• determining an optical response of an adsorbate associated with a nanoparticle as a function of a chemical parameter;
• and
• parameterizing the optical response to produce a one-dimensional representation of at least a portion of a spectral window of the optical response in a high dimensional vector space, wherein the chemical parameter is pH and the optical response comprises a surface enhanced Raman scattering (SERS) spectral response that is a function of pH over at least about 5 pH units and wherein the adsorbate comprises more than one pH sensitive functional group.

A composition comprising a nanoparticle and at least one adsorbate associated with the nanoparticle, wherein the adsorbate displays a chemically responsive surface enhanced Raman scattering (SERS) spectral response that is a function of pH over at least 5 units, wherein the composition is operable as a pH sensor and wherein the optical sensor a pH resolution of about 0.1 pH units.